Retrograde ejaculation is when the semen goes back into the bladder instead
out thru the penis.  It's a common side effect of some BPH medications and
some surgical prostate repair procedures.  It causes no harm and some claim
the orgasm doesn't feel any different, though some say it does.

Look around you at the number of men with very large stomachs. They suffer
from Retro and have made themselves pregnant but are unable to give birth:-)
A heavy burden to carry for life.
Derek.

First question I'd ask:  "Are you on blood pressure lowering medications?"
That may speak to the volume question you raise.  If not, then the following
might apply:

You can get retro in two "general" ways:  medications that relax the urethra
channel and by surgery of the prostate.  Medications try to be selective to
relax the channel so you can urinate when you need to, but meds are not
perfect. Though you have a hard-on, the relaxed muscles in the passageway
may not synchronize enough to ejaculate out of the tip of the penis.  When
you have an orgasm, very little or nothing comes out and, instead,  the
ejaculate flows backwards (retro) into the bladder.  You'll piss it out
later.   Surgery has to cut away at the obstructing prostate and sculpt it
so that as it heals and grows back it will not obstruct the urinary
passageway.  That sculpting process will typically cause ejaculate to flow
backwards.  Retro is not harmful or damaging unless you are trying to father
children.  In that case, go talk to a doctor and they may extract the semen
in alternative ways.    No harm to the body from retro.

As for volume, if you are not on any blood pressure medication, and the
above two conditions do not apply to you, then something else is MIGHT be
taking place?  Best to discuss with doctor if you have any concerns.